An Inductor-Capacitor voltage controlled oscillator (LCVCO) is a linear or harmonic oscillator that generates a sinusoidal waveform. The LCVCO includes a resonator with an inductor L and a capacitor C. In some applications, the LCVCO includes a varactor that can be used to change the capacitance and hence the frequency of an LC tank. The varactor's capacitance is controlled by the voltage across the varactor device to control the resonant frequency in some applications. However, the LCVCOs using varactors to control the operating frequency have a relatively limited frequency tuning range, smaller than 15% of the oscillation frequency in some LCVCOs.
In some applications, multiple LCVCOs with different operating frequencies are multiplexed to cover a relatively wider range of frequency operations. Such multiplexed LCVCOs have performance and design shortcomings as power supply voltages decrease and the operating speeds increase. For example, some LCVCO multiplexer circuits face voltage headroom (margin) issue with a decreased power supply voltage and/or operating speed limit due to the circuit structure.